This section describes how the test program is controlled. The Sequencer (Figure 46) controls the Program Counter. It determines the next step to be executed. Sequencer inputs include the Control Memory, the 16-bit D register, and 16 compared External Event inputs.
Memory Management Block Diagram
Each step includes one command residing in Control Memory. Sequencer commands allow test ware to control and manipulate the Program Counter. Each memory step may include at most one Sequencer command. Most commands can be conditioned.
The Program counter can also be loaded with memory addresses stored in Registers A or B. Addresses are loaded from the PC bus. The figure below displays a block diagram of this process.
Loading Addresses from Registers A and B
The Trigger command causes the board to change to the Run state. Trigger can originate from the following sources:
● Software (Testware)
● External trigger control line
● External event lines (16 lines)
Software Trigger
The software trigger originates within the PC. The PC bus trigger command takes effect immediately, and overrides other established trigger conditions. This happens when the DioTrig command is called from the Driver.
External Trigger
External Trigger Control Line
External triggers originate from the External Trigger line. Pulling this line low causes the board to enter the Run state. The External Trigger line overrides other set trigger conditions.
External Event Lines
It is also possible to set a conditional trigger command activated upon receiving external event inputs. This external event may be any expected value on all or part of the external event input lines. The 16 external event lines are ANDed with pre-defined masks and compared with predefined events in registers D and T.
The external event trigger function is displayed in the figure below.
External Events Trigger Block Diagram
The external event trigger can be set to one or two levels. In the one level mode the trigger generates after the external condition have been met subject to the D or T event mask register. In the two level mode, the board waits for two sequential event conditions before issuing the trigger signal (D first, T second or vice versa).
Pause Command
The Pause command causes the board to enter the Pause state. It originates from the following sources:
● Software
● External control line (XPAUSE on J1)
● External events line
● Sequencer command
External Pause Control Line
External Pause is activated when the external pause line goes low. This causes an immediate pause. The external pause condition overrides internally generated pause conditions.
External Pause Event Lines
The External/Internal Events pause function is displayed in the figure below. The P mask and event registers can be used to create conditional pauses that depend on external event lines. The 16 external event lines are ANDed with predefined masks and compared with pre-defined events in register P.
External Events Pause Block Diagram